Molecular dynamics for very large systems on massively parallel computers: The MPSim program

We describe the implementation of the cell multipole method (CMM) in a complete molecular dynamics (MD) simulation program (MPSim) for massively parallel supercomputers. Tests are made of how the program scales with size (linearly) and with number of CPUs (nearly linearly) in applications involving up to 10⁷ particles and up to 500 CPUs. Applications include estimating the surface tension of Ar and calculating the structure of rhinovirus 14 without requiring icosahedral symmetry. © 1997 by John Wiley & Sons, Inc.     

Ir- spectroscopy of hydrogen bond as a method of analytical determination of physical network in poly(ether urethane)s

The equilibrium association of urethane groups in a series of 4, 4′ - diphenylmethane diisocyanate (MDI)/polypropylene oxide) (PPO) based poly(ether urethane) elastomers (PUE) was studied on the basis of IR-spectroscopy data. The concentration of associates containing 2,3 and 4 urethane groups is calculated, which permits immediate monitoring of changes in PUE mechanical properties using the model of a physically cross-linked polymer.     

Nitrogen-Based Linkers with a Mesitylene Core: Synthesis and Characterization

Mesitylene was used as a core in seven new tritopic nitrogen containing linkers. Three of the linkers, each containing three nitrile groups, were obtained through Suzuki, Sonogashira and Heck-type coupling reactions. Next, these were converted to tetrazol-5-yl moieties by the cycloaddition of sodium azide to the nitrile functionalities. The last linker, containing three 1,2,3-triazol-4-yl moieties, was synthesized by the Huisgen cycloaddition of phenyl azide to the corresponding alkyne. The latter was obtained via a Corey–Fuchs reaction sequence from the previously reported formyl derivative. As the proof of concept for their potential in MOF design, one of the nitriles was used to build an Ag-based network.     

VIP-2 —High-Sensitivity Tests on the Pauli Exclusion Principle for Electrons

The VIP collaboration is performing high sensitivity tests of the Pauli Exclusion Principle for electrons in the extremely low cosmic background environment of the underground Gran Sasso National Laboratory INFN (Italy). In particular, the VIP-2 Open Systems experiment was conceived to put strong constraints on those Pauli Exclusion Principle violation models which respect the so-called Messiah–Greenberg superselection rule. The experimental technique consists of introducing a direct current in a copper conductor, and searching for the X-rays emission coming from a forbidden atomic transition from the L shell to the K shell of copper when the K shell is already occupied by two electrons. The analysis of the first three months of collected data (in 2018) is presented. The obtained result represents the best bound on the Pauli Exclusion Principle violation probability which fulfills the Messiah–Greenberg rule.     

Photoluminescence of GeSi/Si(0 0 1) self-assembled islands with dome and hut shape

The photoluminescence spectra of GeSi/Si (0 0 1) self-assembled islands produced by solid source molecular beam epitaxy in a wide range (460–700°C) of growth temperatures were investigated. The results showed a blue shift of the island-related photoluminescence peak with a growth temperature lowering from 600°C to 550°C. The observed blue shift of the island photoluminescence peak is associated with a sharp decrease in the average height of the island, which occurs through a change of its shape from dome to hut as the growth temperature lowers from 600°C to 550°C.     

Perron Conditions for Uniform Exponential Expansiveness of Linear Skew-Product Flows

 We present necessary and sufficient conditions for uniform exponential expansiveness of discrete skew-product flows, in terms of uniform complete admissibility of the pair (c ₀(N, X), c ₀(N, X)). We give discrete and continuous characterizations for uniform exponential expansiveness of linear skew-product flows, using the uniform complete admissibility of the pairs (c ₀(N, X), c ₀(N, X)) and (C ₀(R ₊, X), C ₀(R ₊, X)), respectively. We generalize an expansiveness theorem due to Van Minh, R?biger and Schnaubelt, for the case of linear skew-product flows.     

Modeling,design, growth and characterization of red wavelength range microcavity emitters for plastic optic fiber applications

Resonant cavity light emitting diodes (RC-LEDs) and vertical cavity surface emitting lasers (VCSELs) for the red wavelength range are presented in the paper. A wide variety of simulation tools were employed in the device design and optimization and the good agreement between simulations and measurements enabled effective device development. Our red wavelength range RC-LEDs were mainly intended for short-haul communication systems based on polymethyl methacrylate plastic optical fiber and were optimized accordingly. They are achieving, under different structure and working regime variants, high output power (15 mW), high external efficiency (9.5%), record small-signal modulation bandwidth (f _-3dB up to 350 MHz), error-free back-to-back transmission rates beyond 622 Mbits/s, adjustable far-field pattern and good POF coupling efficiency with reasonably wide tolerances and without using auxiliary optics. In view of the possible use of graded-index POFs, free-space transmission and other high bandwidth or high spectral purity applications, VCSELs in the red wavelength range were also realized. They have achieved sub-milliamp room-temperature (RT) continuous-wave (CW) lasing for an 8 m diameter emission window and exhibited an external quantum efficiency of 6.65% for 10 m devices in RT CW operation. The VCSEL structures were far from optimal – not even incorporating all the RC-LED structure refinements – and significant improvement in performance characteristics are predicted for the optimized layer structure.     

A gauge model with confinement in four dimensions

It is shown that the correctly written “1/k⁴” propagator in four space-time dimensions leads to a consistent pertubative expansion of a superrenormalizable (asymptotically free) abelian gauge model. Confinement is found in any order of perturbation theory. A discussion of the physical space is sketched and the violation of asymptotic completeness is pointed out.     

Stability and robustness properties of a class of discrete–time residual generators

The aim of this paper is to present a design methodology for an observer–based fault detection filter. This approach allows to compute a filter gain such that both fault detection and disturbance attenuation requirements are accomplished. The developments are based on H_∞ optimization in the discrete–time framework. The existence conditions for the observer–based detection filter are expressed in terms of feasibility of a system of matrix inequalities. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self-diffusiophoresis of chemically active colloids

Chemically active colloids locally change the chemical composition of their solvent via catalytic reactions which occur on parts of their surface. They achieve motility by converting the released chemical free energy into mechanical work through various mechanisms, such as phoresis. Here we discuss the theoretical aspects of self-diffusiophoresis, which – despite being one of the simplest motility mechanisms – captures many of the general features characterizing self-phoresis, such as self-generated and maintained hydrodynamic flows “driven” by surface activity induced inhomogeneities in solution. By studying simple examples, which provide physical insight, we highlight the complex phenomenology which can emerge from self-diffusiophoresis.